The gangrenous and convulsive ergot syndromes that can follow the ingestion of C. purpurea have long been known. Art depicts the classic signs and symptoms of poisoning, such as the strange dancing syndrome shown in woodcuts from the middle ages in Germany and Poland.
The Temptation of St Anthony, a famous painting by the German artist Matthias Gr√ºnewald, depicts people with gangrenous digits, lurid rashes, ulcerations and dystonic postures. At the time of the painting, circa 1500 AD in the middle ages, this condition was known as St Anthony’s Fire.
From Mike Schachter’s chapter in Ergot-derived Drugs: A Cross Therapy Evidence-based Review (ISBN 1853156140).
Albert Hoffman discovered LSD when researching ergot, and LSD is still synthesised from ergot today.
Mind Hacks 
There is a 1968 book written by John G. Fuller, titled _The Day of St. Anthony’s Fire_. It’s out of print now, but it details the true story of Pont-St.-Esprit, a tiny Provencal village where the boulangerie’s flour was contaminated with ergot. People and animals which had eaten the bread baked with the tainted flower went beserk. I read this book in high school and never forgot it.
The book is out of print now, but you can still find some used hardcover versions of the book on Amazon.
If I remember from the Scientific American circa 1969, there are several different natural compounds in ergot fungus from rye, as well as two families (Tetracyclic Ergolines, and Peptide Alkaloids) with about 8 chemically interesting products. I believe only one natural compound is soluble in water; LSD 2. The water soluble compound would evaporate in an oven, so whatever St. Antony’s Fire is, must come from some combination of the others. The effects should not properly be blamed on LSD 2.
There is a lot of speculation about ancient ritual use of LSD 2. It seems to be a relatively benign compound, not as intense as LSD 25. I have no knowledge of anyone actually using it though.